Biopsy location for direct immunofluorescence in patients with suspected bullous pemphigoid impacts probability of a positive test result.

Background: Bullous pemphigoid (BP) is an autoimmune polymorphic skin disease characterized by erythematous papules and plaques and tense bullae. A skin biopsy for direct immunofluorescence (DIF) is used to detect autoantibodies and complement proteins.

Objective: We sought to determine which location would provide the highest probability of obtaining a positive DIF result.

Method: We undertook a retrospective chart review of 1,423 DIF biopsies. Biopsies with a clinical suspicion of BP were designated as either lesional, perilesional, or indeterminate.

Results: Fifty percent of lesional DIF biopsies were positive, whereas 22% of perilesional and 12% of indeterminate biopsies had a positive DIF result. The odds ratio of a positive DIF from a lesional versus perilesional biopsy site was found to be 3.45 (95% CI 1.44-8.29).

Conclusion: Clinicians are more likely to obtain a positive DIF result from a lesional nonbullous skin biopsy than from a perilesional or normal skin biopsy.